Such filter devices are particularly used for the filtration of polymer meltings and liquids. The fluid is led through filter chambers, each of which comprises at least one respective filter element which eliminates dirt, contaminants or conglomerates contained in the fluid. When the filter element is contaminated, it has to be replaced, for which purpose the filter support element, which is movably mounted in a bore hole in the housing, can be shifted to a filter replacement position.
From DE 102 54 022 a filtering device is known which comprises two filter support elements with two respective filter positions. When one filter support element is shifted to a maintenance position in order to clean the filter chamber and the filter element, the filters of the other filter support element are available for filtration. By skillfully guiding the inlet and outlet channels in the housing it is even possible to accomplish a filtration on the filter support element which is in the maintenance position when using the filter chamber that is currently not maintained, so that at least 75 percent of the filter surface are constantly available, while in the other filter element back flushing takes place, in that fluid is led through the filter element from the clean side, which is then discharged to the outside with all adhering contaminations via a back-flush channel.
In order to increase the achievable flow capacity, or the filterable fluid volume per time, with the filter device, it is generally necessary to increase the filter surface. For this, it is possible to increase the size of the entire filtering device which, however, considerably increases the costs. There are other approaches for using filter units, by means of which it is possible with the use of stacked filter discs to provide larger filter surfaces while the filter chambers have the same opening areas. However, the latter units are not suited for all kinds of liquids to be filtered.
Another problem involves the processing of sensitive fluids, which change chemically during longer dwell times, in particular when they flow into the gap between the filter support element and the bore hole of the housing. For example, there is even the danger of explosion in the processing of so-called textile pulp for synthetic fibers, when fluid residues stagnate locally for such a long time, that they can react with iron atoms dissolved from the filtering device. Therefore, EP 915 729 B1 suggests to adjust the filter support and the bore hole of the housing in such a way that a flow-gap is formed between the two. To ensure that the filter support stays in the center of the bore hole and is not pressed by the dynamic pressure to one side of the outlet channel, special distance holder elements are provided on the filter support element.